Buy All the Bug Spray: An Aggressive New Mosquito Is Buzzing Around

Gimena Ruedas is rummaging among the trash cans of an old Craftsman home in South Pasadena. “We usually require that all the trash bins have holes in them,” she says. “Everything in the yard has to drain completely. Anything that can hold the amount of water that can fit into a bottle cap—that’s all they need to grow.” By “they” Ruedas means mosquitoes, but not just any: An assistant ecologist with San Gabriel Valley Mosquito & Vector Control, she’s on the hunt for the eggs and larvae of the Aedes aegypti, the most recent invasive bloodsucker to be detected in the region. After first turning up in Central California in 2013, it spread south, arriving in the San Gabriel Valley last year.

That’s fast. Experts chalk up the speedy progression to the mosquito’s ferocity and durability. Where most mosquitoes eschew air-conditioned environments, the aegypti does not, and while native mosquitoes limit mealtimes to the evening, the newcomers bite day and night. “These guys are so aggressive that they will follow people into their cars,” Ruedas says as she pokes around a bag of potting soil (moist soil and leaves are breeding grounds, too) for eggs and larvae. Residents in the area first noticed them a few months earlier, once they started being mauled whenever they went into their yards. “People can’t go out and have barbecues because they’re getting bit up,” she says.

This is new terrain for Southern California, a part of the world that’s enjoyed far fewer insects than others. “We were spoiled all these years,” says J. Wakoli Wekesa, the scientific program manager at San Gabriel Valley Mosquito & Vector Control at the time of Ruedas’s visit. (He’s since moved on to Coachella Valley Mosquito & Vector Control.) As Wekesa notes, the Aedes aegypti isn’t new to the U.S.; it’s just new here. The mosquito probably came stateside from Africa during the slave trade. “There was an effort to eradicate it,” he explains. “They say it was eradicated in most of the Americas until the 1960s, when the U.S. abandoned that effort during the Kennedy administration.” That was when the chief pesticide used to kill mosquitoes, DDT, was banned because of the environmental havoc it wrought.

Of course, as pesky as mosquitoes are, the reason Ruedas is poking around this yard is because the insects can be deadly. The Aedes aegypti is the primary transmitter of the Zika virus, which can cause underdeveloped brains in fetuses. So far no cases have been transmitted here, but all it takes is for one mosquito to pick up the virus from an infected host and spread it. That’s how West Nile virus got established here in 2003 among native mosquitoes. Last year 153 people were diagnosed with the illness; five died.

There are other pestilential concerns, among them dengue fever and chikungunya, a virus that swept through the Caribbean a few years ago. Not only can aegypti transmit them, so can the Aedes albopictus, better known as the Asian tiger mosquito (the aegypti is known as the yellow fever mosquito in parts of the world where that malady is common). Pinpointed here in 2011, this other invasive species also bites day and night and can carry Zika; it’s just not the primary vector for the disease. Aegypti is.

Hence the once-over Ruedas is giving this property. After homing in on the opening to a rain barrel (“the mosquitoes can squeeze through the screens on top”), she reaches into her satchel and produces a water-filled vial. Inside, larvae wriggle in the sunlight. “I grew up thinking they were tadpoles,” she says. The cloudless 103-degree day has left a sheen of sweat on her forehead, but Ruedas is wearing a long-sleeved shirt and pants. “It’s really hot,” she says, a wide-brimmed straw hat offering meager shelter. “We’re not like the mailman, who gets to wear shorts. They’ll bite through your clothing and get down to your skin, even with the long sleeves and long pants and loose clothing.”

In truth South Pasadena isn’t part of San Gabriel Valley Mosquito & Vector Control’s official turf; Ruedas was sent out after residents pleaded with Wekesa back at HQ. Born in Kenya, Wekesa grew up watching another mosquito-born illness, malaria, ravage the land. “Children under five were quite vulnerable, and now I understand why society rarely celebrated the second, third, or fourth birthday of a child,” he says. That’s why he’s in the business of battling mosquitoes today. Though the aegypti and albopictus haven’t spread to the Westside yet, he says that it’s just a matter of time. They might actually prefer the cooler climate there. “Our lifestyle changes going forward. No doubt about it,” he says, “and how we’re going to adapt in this coming environment is going to be a challenge to all of us. I don’t think we are ever going to reverse this invasion.”